Classic computer stereovision systems use two imagers such as cameras to shoot pictures of the same scene from different angles. The cameras are separated by an interocular distance, and are synchronized. A computer then calculates depths of objects in the scene by comparing images shot by the two different cameras. This is done by shifting one image on top of the other one to find the parts that match. The distance or amount the images must be shifted to find a best match is called the disparity. The disparity at which objects in the images best match is used by a computer to calculate their depths and provide a three-dimensional image of the scene.
A multi-view imaging system uses only one camera to calculate the object depth. In most cases, such a system uses specially designed mirrors or prisms to create virtual cameras. With the views captured by the real camera and the virtual cameras side-by-side or one above the other, the computer can use the same scheme as in classic computer vision to calculate the depth of an object.
In prior art multi-view imaging systems, two pairs of flat reflectors such as mirrors are used to define two light channels: a left channel and a right channel, encased in a dust and light proof housing device that fits in front of a camera lens in the same manner as a close-up accessory or telephoto adapter (see FIG. 1). Within each channel, one of the mirrors takes incoming light rays and reflects the light rays to the other mirror for it to output the light rays to an imager such as a camera, CCD, etc. through the lens. The mirror that takes the incoming light rays will be called an outward mirror (describing the orientation of the mirror relative to the incoming light rays and the imager) and the mirror that outputs light rays to the camera will be called an inward mirror. The inside vertical edges of the two inward mirrors are connected along the optical axis of the imager lens (see FIG. 1). Light rays into the left channel will generate a left view of the scene on the right half of the imager and light rays into the right channel will generate a right view of the scene on the left half of the imager. The device permits acquisition of simultaneous left and right views using a single imager. Such a device has been called a two-channel reflector (TCR).
To adjust the convergence angle of the optical axes of the virtual cameras, it is known to provide a TCR that allows a user to swivel the outward mirrors simultaneously and equally about their inside vertical edges with a ganging mechanism. A disadvantage of this approach is that making the convergence angle of the optical axes of the virtual cameras smaller (i.e., making the convergence point further away from the imaging system) also makes the interocular distance between the virtual cameras smaller and consequently lowers the disparity between the left view and the right view.
Improvements in the above design are also known, wherein the basic idea is to swivel the outward mirrors about their vertical centerlines, instead of the inside vertical edges. The advantage of this approach, in addition to adjusting the convergence angle of the views of the left virtual camera and the right virtual camera, is that it reduces the impact of the disparity reduction by one half.
Other prior art devices also allow the inward mirrors to be swiveled about their connected inside edges activated by rods connecting the inward mirrors and the outward mirrors. In these cases the outward mirrors could be swiveled about their inside edges instead of their centerlines. Location of the connected inside edges of the inward mirrors is fixed. However, the swiveling process of these prior art devices has not been mathematically modeled or characterized.
Another prior art two-channel reflector based multi-view imaging system includes a single hand held CCD mounted on a two-channel reflector. Like a typical TCR, light rays into the left channel generate a left view of the scene on the right half of the CCD and light rays into the right channel generate a right view of the scene on the left half of the CCD. Hence, an image generated by this imaging system contains two views of the scene, a left view and a right view. These views are used in camera calibration and correspondence estimation to obtain an accurate 3D model of the scene. A user can adjust the convergence angle of the virtual cameras by adjusting the outward mirrors about their centerlines. Like all the TCR models that have been developed so far, the disparity can be adjusted only as a side effect of adjustment of the convergence angle.
A stereographic imaging system with automatic control of interocular distance is known, but is a two-camera system. The system includes a left camera and a right camera with respective lenses. The system also includes mechanisms to synchronously set a focal length of the lenses, to synchronously set a focal distance of the lenses, to set a convergence angle between the left and the right cameras, and to set an interocular distance between the left and right cameras. A controller may determine a convergence based on the focal length. The controller may cause an interocular distance and a convergence angle between the left and right cameras to be set based on a maximum allowable disparity, the focal length of the lenses, the convergence distance, and a distance to an object in the scene. This is so far the only stereographic imaging system with the capability of direct control of both the convergence angle and the interocular distance (and so disparity) of the imaging process.
To the author's knowledge, no single lens multi-view imaging systems are available providing control of both convergence angle and interocular distance. In turn, to the author's knowledge no imaging systems providing the capability of switching between 2D and 3D modes are available.